Optical transparent dual cure adhesives composition

ABSTRACT

The present invention relates to an optical transparent dual cure adhesive, and process for preparing this dual cure adhesive, and uses thereof. More particularly, the present invention relates to optical transparent adhesive, which is both capable of being UV-light cured and thermal cured, for example, it can be used for the bonding of touch screen of an electronic device and substrate.

The present invention relates to an optical transparent dual cureadhesive composition, and process for preparing the dual cure adhesivecomposition, and uses thereof. More particularly, the present inventionrelates to optical transparent adhesive composition, which is both UVcurable and thermal curable. For example, it can be used for the bondingof touch screen and substrate of an electronic device.

UV curable (abbreviated as UV cure) adhesives were reported in the1960s, since then considerable achievements were achieved through anextensive research. UV cure adhesives refer to adhesives that may curerapidly under UV radiation. Today, UV cure adhesives have beensuccessfully applied in many fields of industrial assembly, especiallyhigh-tech industries where fast assembly is required, such as liquidcrystal display (LCD) manufacturing, cameras and other optical productsmanufacturing, CD manufacturing, watch-making industry, mobile phonekeypad assembly, electronic circuit board manufacturing, electroniccomponents manufacturing in optoelectronic information industry such asmanufacturing of the polarized components. UV cure adhesives are alsowidely used in the commodity sector, such as the manufacturing of glassfurniture, assembly of glass crafts, assembly of toys, jewelry and otherdecorations, since a high and efficient productivity can thus beachieved.

For example, Zhang Nanzhe and Xu Sulian reported “Application of UVcurable adhesive in manufacturing of LCD” (Journal of ChangchunUniversity of Science and Technology, 2005(4)), where the application ofUV curable adhesives in manufacturing of liquid crystal displays (LCD)as well as the technical requirements were studied.

In adhesion of touch screen components and substrate of LCD products,for example, 3M Innovative Properties Company filed a PCT application WO2010/111316 A2 on Mar. 24, 2010. WO 2010/111316 A2 is directed to anoptical assembly having a display panel, wherein an adhesive layer oradhesive composition is used as the display panel, so that the displaypanel is bonded to the substantially transparent substrate. The adhesivelayer comprises the reaction product of a multifunctional (meth)acrylateoligomer, a reactive diluent comprising a monofunctional (meth)acrylatemonomer; and a plasticizer, wherein the reaction product in the adhesivelayer can be obtained by initiating polymerization usingUV-photoinitiators.

However, in some specific application fields using the conventional UVcurable adhesives, some problems may be encountered. For example, shadowareas may exist between the liquid crystal panel and the substrate, thatis, areas that light cannot transmit or penetrate, UV/visible lightcannot transmit through these areas, thus the adhesives cannot be curedcompletely, and may cause problems such as corrosion, aging fatigue orpeeling of unbonded edges. Generally, the shadow areas are for examplethe edge areas where ink coatings exist, and etc.

Since the current commercial available UV-curable adhesive could notmeet above demands, there is a need, therefore, to overcome suchdefects.

One solution to above problems is to combine adhesives having differentcure mechanisms, such as dual cure mechanism adhesive.

As to dual cure mechanism adhesive, for example, the following types ofadhesive compositions were reported:

In U.S. Pat. No. 7,688,551 B2 (the contents thereof are incorporatedhere by reference), Alexander P. Mgaya et al propose a dual curemechanism adhesive, wherein one cure mechanism is based on the drying ofthe adhesive, which is mainly due to the evaporation of water or othervolatile substances in emulsion of adhesive components; the other curemechanism is UV or visible light irradiation. This adhesive has thefollowing components: a water-based emulsion; (meth)acrylatefunctionalized monomer capable of polymerizing or crosslinking; and atleast one UV-photoinitiator; wherein said water based emulsion is curedor crosslinked by water evaporation/coagulation.

In addition, in U.S. Pat. No. 5,997,682 (the contents thereof areincorporated here by reference), Daniel L. Gooman et al propose aphase-separated dual-cure elastomeric adhesive formulation,characterized in that the dual cure elastomeric adhesive is E-beam curedand heat cured at relatively low temperature; this adhesive can be usedfor bonding structure which is thick or has irregular shapes, forexample, the structural parts in automobile or aeroplane havingirregular shapes. This adhesive mainly comprises: urethane acrylateoligomer sensitive to irradiation; reactive dilute sensitive toirradiation; hydroxy group containing compounds, such as saturatedpolyol; compounds containing isocyanate functional group, such aspolyisocyanate, or urethane prepolymer. This patent proposes to rotatethe structure to be bonded, and e-beam irradiation is conducted for twoor more times and heat cure is conducted at relatively low temperaturefor a certain period of long time, so as to cure the adhesivecompletely.

In U.S. Pat. No. 5,696,209 (the contents thereof are incorporated hereby reference), Russell K. King et al propose dual cure silicone adhesivecomposition, which is solventless dual cure organosilicon adhesive,flowable or extrudable at room temperature. The adhesive is firstreacted by addition to cure into viscous and sticky state; then it iscondensed to cure slowly (moisture cure), obtaining non-flowable bondedbody with high bonding strength. This patent further proposes moisturecure the addition cured product, to form a permanent cured body.

In U.S. Pat. No. 4,605,465 (the contents thereof are incorporated hereby reference), Charles R. Morgan et al propose a composition containingthermoplastic material which is UV curable and also thermal curable;wherein the disclosed adhesive composition comprises:

Liquid ethylenically unsaturated monomer, prepolymer or polymer havingthe following repeating unit of:

wherein thermal initiator, UV-photoinitiator, thermoplastics, forexample, vinyl resin, such as PVC, PVDC, and PS; un-polymerizableplasticizer are used; and the thermoplastics is in the form ofdispersion in the plasticizer, wherein the use of thermoplastics andplasticizer cause the unsaturated monomer, prepolymer or polymer havingacrylate group would not lead to a sticky surface upon UV irradiation.Optional component includes reactive dilute, such as monofunctionalacrylate, and the heating step requires a condition of at least 80° C.,preferably 80-200° C., so as to obtain a full cure product.

However, all above dual cure adhesives could not be used to solve theproblem of the present invention, i.e., when shadows exist between thetouch screen and substrate, that is, portions or areas that light orrays could not penetrate, adhesive can not be cured completely, which inturn leads to problems, such as corrosion, aging fatigue or peeling ofunbonded portions.

Therefore, it is an object of the invention to provide an opticaltransparent dual cure adhesive composition, which should be able tosolve all the above problems.

A first subject matter of the present invention is an opticaltransparent dual cure adhesive composition, based on the total weight ofthe adhesive composition, the composition comprises:

10-90 wt % of photo curable oligomer or polymer having (meth)acryloxygroup or vinyl group;

5-55 wt % of (meth)acrylate;

0-50 wt % of liquid polybutadiene;

0.5-5 wt % of UV-photoinitiator; and

0.5-5 wt % of thermal initiator.

In another aspect of the invention, there is provided an opticaltransparent dual cure adhesive composition, based on the total weight ofthe adhesive composition, the composition comprises:

40-90 wt % of urethane oligomer having (meth)acryloxy group;

5-55 wt % of (meth)acrylate;

0.5-5 wt % of UV-photoinitiator; and

0.5-5 wt % of thermal initiator.

In another aspect of the invention, there is provided an opticaltransparent dual cure adhesive composition, based on the total weight ofthe adhesive composition, the composition comprises:

10-80 wt % of polyisoprene having (meth)acryloxy group or vinyl group;

10-55 wt % of (meth)acrylate;

0-50 wt % of liquid polybutadiene,

0.5-5 wt % of UV-photoinitiator, and

0.5-5 wt % of thermal initiator.

In another aspect of the invention, there is provided a process forpreparing the adhesive composition as mentioned above, comprising thesteps of:

under the condition of darkness, according to a predetermined ratio,feeding each components of an adhesive composition into the mixingcontainer; conducting mixing under agitation for a sufficient time, soas to homogenize each components; thus obtaining the adhesivecomposition.

Another aspect of the invention also relates to the uses of the adhesivecomposition for bonding a touch screen and substrate of an electronicdevice.

The term “cure” or “curing” as used herein refers to a change in state,condition, and/or structure in a material that is usually, but notnecessarily, induced by at least one variable, such as time,temperature, moisture, radiation, presence and quantity in such materialof a cure catalyst or accelerator, or the like. The terms cover partialas well as complete cure. For purposes of the present invention, theterms mean at least partially crosslinked, and in more preferredembodiments substantially or fully crosslinked.

The term “dual cure” used herein refer to UV cure induced by usingUV-photoinitiator as well as thermal cure induced by using thermalinitiator, the UV light cure refers to a cure under the irradiation ofUV light for a certain period of time, and the thermal cure refers to acure under certain temperature for a certain period of time.

Unless stated otherwise, all percentages, parts, ratios, etc., are byweight.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. In case of conflict, thepresent specification, including definitions, will control.

When an amount, concentration, or other value or parameter is given aseither a range, preferred range or a list of lower preferable values andupper preferable values, this is to be understood as specificallydisclosing all ranges formed from any pair of any lower range limit orpreferred value and any upper range limit or preferred value, regardlessof whether ranges are separately disclosed. Where a range of numericalvalues is recited herein, unless otherwise stated, the range is intendedto include the endpoints thereof, and all integers and fractions withinthe range.

Hereafter, technical terms or expressions involved in preferredembodiments will be described, in which the embodiments are just for thepurpose of illustrating the present invention rather than limiting thepresent invention.

“Photo curable oligomer or polymer having (meth)acryloxy group or vinylgroup” is a functionalized oligomer or polymer, on the molecular chainthereof, there exists (meth)acryloxy group or vinyl group reactive to UVlight irradiation. These oligomer or polymer is a polymer preferablyhaving low to medium molecular weight, for example, usually saidfunctionalized oligomer or polymer can have number average molecularweight of about 300 to about 50000 Daltons, preferably 800-40000Daltons, more preferably 1000-35000 Daltons, more preferably 3000-25000Daltons, more preferably 5000-20000 Daltons. Said (meth)acryloxy and/orvinyl functional group could be located at the end(s) of the polymerchain, or may be distributed along the polymer chain thereof. Thefunctional group(s) on said functionalized oligomer or polymer chaincurable by irradiation preferably have average degree of functionalityof more than 0 to less than or equal to 3, especially from 0.5 to 2.5.Herein the term “average degree of functionality” refers to the averagenumber of (meth)acryloxy group or vinyl functional group permacromolecular chain.

The non-limited but preferred examples of said oligomer or polymerinclude (meth)acryloxy group functionalized urethane oligomer, such as(meth)acryloxy group functionalized polyether urethane, and(meth)acryloxy group functionalized polyester urethane, polyisoprenehaving (meth)acryloxy group or vinyl group and the like. These oligomeror polymer and preparation thereof are known in art, for example, pleaserefer to the disclosures in U.S. Pat. Nos. 4,574,138, 4,439,600,4,380,613, 4,309,526, their entire contents are incorporated here byreference.

Based on the total weight of the adhesive composition, the adhesivecomposition contains 10-90 wt % of said functionalized photo curableoligomer or polymer, preferably 20-85 wt %, more preferably 30-70 wt %.

The structure of (meth)acryloxy group is CH₂═CRC(O)O—, wherein R is H orCH₃. The term “(meth)acryloxy group” represents acryloxy, methacryloxygroup or their combination; the term “(meth)acrylic acid” representsacrylic acid, methacrylic acid or their combination; the term“(meth)acryl” represents acryl, methacryl or their combination, and soon,

“Urethane oligomer having (meth)acryloxy group” is a specific andnon-limited but preferred example of the photo curable oligomer orpolymer having (meth)acryloxy group or vinyl group, which is an urethaneoligomer having (meth)acryloxy group, and sometimes it is also referredto as urethane (meth)acrylate oligomer.

The urethane oligomer having (meth)acryloxy group preferably has anaverage degree of functionality of more than 0 and equal to or less than3; more preferably 0.5-2.5.

The urethane oligomer having (meth)acryloxy group preferably has anumber average molecular weight of 1000-25000 Daltons, more preferably1500-10000 Daltons, even more preferably 2000-8000 Daltons.

The urethane oligomer having (meth)acryloxy group in accordance with thepresent invention preferably has a T_(g) of from −80 to 0° C., morepreferably from −60 to 0° C. Said urethane oligomer having(meth)acryloxy group preferably has a Brookfield viscosity of 1000centipoise (cps) to 190000 cps, more preferably from 2000 cps to 150000cps; even more preferably from 5000 to 100000 cps at a temperature of25° C. at a shear rate of 2.55 s⁻¹, measurable by HAAKE RotationalRheometer with a cone plate (35 mm diameter).

Useful and preferred urethane oligomer having (meth)acryloxy groupincludes commercially available products, for example, said urethaneoligomer may preferably include: urethane diacrylate CN9018, CN9021,CN3108, CN3211, CN8004 commercially available from Sartomer, Co., Exton,Pa.; GENOMER 4188/EHA (mixture consisting of 80 wt. % of amonoacrylate-functional polyesterbased oligomer comprising at least oneurethane bond, and 20% 2-ethylhexyl acrylate monomers; the oligomercomprised by GENOMER 4188 has a weight average molecular weight Mw ofabout 8,000), GENOMER 4188/M22 (mixture of GENOMER 4188 and GENOMER 1122monomers), GENOMER 4256 and GENOMER 4269/M22 (mixtures of GENOMER 4269and GENOMER 1122 monomers), commercially available from Rahn USA Corp.,Aurora Ill., and etc.

Usually, the amount of said urethane oligomer having (meth)acryloxygroup used in the adhesive composition of the present invention dependsfrom the amounts of the other components used for forming the adhesivecomposition, and the desired properties of the adhesive composition. Theadhesive composition may include about 40-90 wt % of the urethaneoligomer having (meth)acryloxy group, preferably from about 45-85 wt %,more preferably 50-80 wt %, more preferably 60-70 wt %.

Most specifically, examples of the urethane acrylate oligomer used inthe present invention include, for example CN9018, CN9021, CN3108,CN3211, CN8004 from Sartomer Company, Inc.

According to the present invention, the urethane oligomer having(meth)acryloxy group may be used alone or in any desired combination ofseveral urethane oligomers having (meth)acryloxy group; the specifictypes and combination thereof depend from the desired properties of theproducts.

“Polyisoprene having (meth)acryloxy group or vinyl group”: Anothernon-limited example of photo curable oligomer or polymer having(meth)acryloxy group or vinyl group is polyisoprene having(meth)acryloxy group or vinyl group.

Generally, this is an isoprene polymer modified by reactive functionalgroups, for example, polyisoprene grafted with acrylate group, orpolyisoprene grafted with vinyl groups. Wherein the backbone or mainchain of the macromolecule polyisoprene may have a number averagemolecular weight of 10000-50000 Daltons, preferably 12000-40000 Daltons;more preferably 15000-35000 Daltons. As to the grafted reactive groups,this exemplified acrylate functional group or vinyl functional group maybe located at the end(s) of the isoprene oligomer, or may be pendant tobranches of isoprene oligomer.

The polyisoprene having acryloxy or vinyl functional group used inaccordance with the present invention may have a Brookfield viscosity,at a temperature of 25° C. at a shear rate of 2.55 s⁻¹, severalthousands to tens of thousands cps, for example 10000-100000 cps, or15000-80000 cps, or 25000-60000 cps, measurable by HAAKE RotationalRheometer with a cone plate (35 mm diameter).

Specifically, the non-limited examples of polyisoprene having acryloxyor vinyl functional group are as follows: polyisoprene UC203, UC102,commercially available from KURARAY CO., LTD, and the like.

In the adhesive composition in accordance with the present invention,polyisoprene having acryloxy or vinyl functional group can be used in atan amount of 10-80 wt %, preferably 20-70 wt %, more preferably 30-60 wt%.

According to the present invention, in the adhesive composition,polyisoprene having acryloxy or vinyl group may be used alone or in anycombination of several polyisoprenes having acryloxy or vinyl group. Thespecific types and combination thereof depend from the desiredproperties of the adhesive products.

“(Meth)acrylate”: The adhesive composition in accordance with thepresent invention also makes use of (meth)acrylate. Said (meth)acrylateis, for example, aliphatic alkyl(meth)acrylate, and (meth)acrylatehaving epoxy function, and the like. It could be a monofunctional(meth)acrylate, i.e., there is only one (meth)acrylate group within itsmolecule, it could also be a multifunctional (meth)acrylate, i.e., it isa (meth)acrylate having two or more than two (meth)acrylate group withinits molecule.

The (meth)acrylate monomer preferably is monofunctional- andmultifunctional alkyl(meth)acrylates, monofunctional- andmultifunctional alkenyl(meth)acrylates, and monofunctional- andmultifunctional heterocyclo(meth)acrylates. Said alkyl moiety preferablyis an alkyl group having from 1 to 20 carbon atoms, which may furtherhave one or more substituents selected from an alkyl group having from 1to 20 carbon atoms, an alkoxy group having from 1 to 20 carbon atoms, anaryloxy group having from 6 to 20 carbon atoms, an epoxy group havingfrom 2 to 20 carbon atoms, hydroxyl and the like. The alkenyl moietypreferably is an alkenyl group having from 2 to 20 carbon atoms, whichmay further have one or more substituents selected from an alkyl grouphaving from 1 to 20 carbon atoms, an alkoxy group having from 1 to 20carbon atoms, an acryloxy group having from 6 to 20 carbon atoms, anepoxy group having from 2 to 20 carbon atoms, hydroxyl and the like. Theheterocyclic group preferably is a heterocyclic group having from 2 to20 carbon atoms, and having a hetero atom selected from nitrogen andoxygen. The heterocyclic group may have one or more substituentsselected from an alkyl group having from 1 to 20 carbon atoms, an alkoxygroup having from 1 to 20 carbon atoms, an aryloxy group having from 6to 20 carbon atoms, an epoxy group having from 2 to 20 carbon atoms,hydroxyl and the like.

Preferred examples of monofunctional acrylate component areisobornyl(meth)acrylate, tetrahydrofurfuryl(meth)acrylate, alkoxylatedtetrahydrofurfuryl(meth)acrylate, and mixtures thereof.

Preferred examples of multifunctional acrylate component are: ethyleneglycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,4-butanedioldi(meth)acrylate, pentaerythritol tri(meth)acrylate. pentaerythritoltetra(meth)acrylate, trimethylolpropane(meth)acrylate, tetraethyleneglycol di(meth)acrylate and the like, and mixture thereof.

Preferably said (meth)acrylate is selected from the group consisting of:methyl(meth)acrylate, ethyl(meth)acrylate, butyl(meth)acrylate,2-(2-ethoxyethoxyl)ethyl acrylate, tetrahydrofurfuryl(meth)acrylate,lauryl acrylate, isooctyl acrylate, isodecyl acrylate, 2-phenoxy ethylacrylate, 2-ethylhexyl(meth)acrylate, isobornyl(meth)acrylate,dicyclopentenyloxyethyl(meth)acrylate, dicyclopentadienyl(meth)acrylate,2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate,2-hydroxybutyl(meth)acrylate, caprolactone acrylate,morpholine(meth)acrylate, hexanediol di(meth)acrylate, ethylene glycoldi(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritoltetrahydrofuran(meth)acrylate, hydroxylpropyl(meth)acrylate, ethyleneglycol dicyclopentenyl ether(meth)acrylate, and any combination thereof.

Most preferably used (meth)acrylate monomers are selected from the groupconsisting of: isobornyl acrylate, hydroxypropyl acrylate,2-(2-ethoxyethoxy) ethyl acrylate. ethylene glycol dicyclopentenyl ethermethacrylate, and combination thereof.

Usually, the amount of (meth)acrylate component would depend from theamounts of other components used for forming the adhesive composition,and the desired properties of the adhesive composition. In theembodiments of adhesive composition of the present invention, based onthe total weight of adhesive weight, the contents of (meth)acrylate inthe adhesive composition is 5-55 wt %; preferably 10-55 wt %, morepreferably 10-50 wt %, more preferably 20-45 wt %; more preferably 25-40wt %, and most preferably 20-40 wt %.

“Photoinitiator”: According to the present invention, the adhesivecomposition comprises photoinitiator. Said photoinitiator may includeUV-photoinitiator and visible light photoinitiator.

In the context of the present invention, said photoinitiator preferablyrefers to UV-photoinitiator. UV-photoinitiator is well known in the art,and can be used to initiate the photo polymerization of all the abovefunctionalized photo curable oligomer, polymer having (meth)acryloxygroup or vinyl group.

A variety of UV photoinitiators may be employed. UV photoinitiators aregenerally effective in the wavelength range of 200 to 400 nm, andparticularly in the portion of the spectrum that borders on theinvisible light and the visible portion just beyond this spectrum, e.g.from >200 nm up to about 390 nm. Examples thereof may be benzyl ketal,hydroxy ketone, amino ketone, acyl phosphine oxide, and the like.

Photoinitiators that will respond to UV radiation to initiate and inducecure of the (meth)acrylate functionalized curable component, which areuseful in the present invention include preferably benzophenone andsubstituted benzophenones, acetophenone and substituted acetophenones,benzoin and its alkyl esters, diethoxy acetophenone, benzoin methylether, benzoin ethyl ether, benzoin isopropyl ether,N-methyldiethanolamine benzophenone,2-hydroxy-methyl-1-phenylpropan-1-one,2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone,diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, and combinationthereof.

According to the present invention, the UV-photoinitiator may be usedalone, or in any desired combination thereof. Above UV-photoinitiatorsare just for purpose of illustration, rather than limiting theUV-photoinitiator useful in the present invention.

The amount of UV-photoinitiator used, based on the total weight of theadhesive composition, may be 0.5-5 wt %, preferably 1-4 wt %, morepreferably 2-3 wt %.

“Thermal Initiator”: In the adhesive composition according to presentinvention, thermal initiator is to be used to initiate thepolymerization and cure of the composition. Thermal initiator usuallyincludes azo compounds, peroxides, and other thermal initiator(s) wellknown to those skilled in the art, which is capable of releasingradicals under heating conditions, and combination thereof. Preferablyperoxides are used in the present invention. The peroxide useful in thepresent invention preferably includes organic peroxide and inorganicperoxide. Non-limited examples of organic peroxide may beperoxy-dicarbonate, for example di(2-ethylhexyl)peroxydicarbonate; acylperoxide, for example, dilauroyl peroxide; alkyl peroxide, for example2,5-dimethyl-2,5-di(tert-butylperoxy)hexane; peroxyesters, for exampletert-butyl peroxybenzoate, and the like.

Inorganic peroxide is also well known in the art, and non-limitedexamples of organic peroxide may be persulfate, for example, potassiumpersulfate, sodium persulfate and ammonium persulfate, and the like.

In the adhesive composition of the present invention, peroxide thermalinitiator may be used alone, or two or even more peroxides may be usedtogether.

In the adhesive composition of the present invention the thermalinitiator preferably used is organic peroxide, particularly peroxyesters, and the preferred example thereof is tert-butyl peroxybenzoate,as well as alkyl peroxide, the non-limited example thereof is1,1-di(tert-butyl peroxy)-3,3,5-trimethyl cyclohexane.

The amount of the ester peroxide and alkyl peroxide used, based on thetotal weight of the adhesive composition, is 0.5-5 wt %, preferably 1-4wt %, more preferably 2-3 wt %.

“Liquid Polybutadiene”: In accordance with the present invention, theadhesive composition may optionally include liquid polybutadienecomponent. Preferably, the liquid polybutadiene here is an oligomer ofbutadiene, i.e., it is a product obtainable by anion polymerization orcoordination polymerization, and the degree of polymerization, or themolecular weight thereof or viscosity thereof may be controllable byadjusting the initiator, the amount thereof, the chain transfer agent,the amount thereof, and etc.

The liquid polybutadiene may have a number average molecular weight of1000-30000 Daltons, preferably 1500-25000 Daltons, more preferably2000-20000 Daltons, more preferably 3000-10000 Daltons; and theBrookfield viscosity thereof at 25° C. at a shear rate of 2.55 s⁻¹ maybe hundred cps to tens of thousands cps, for example 500 cps-50000 cps,preferably 1000 cps-30000 cps, more preferably 3000 cps-20000 cps, stillmore preferably 5000 cps-15000 cps, measurable by HAAKE RotationalRheometer with a cone plate (35 mm diameter).

The liquid polybutadiene useful in the present invention may be thosecommercially available products, and the non-limiting examples thereofmay be: Polybutadiene Ricon 130, Ricon156, LBR307, LBR305 and etccommercially available from Sartomer Company, Inc.; whereinPolybutadiene Ricon 130 has a number average molecular weight of about2500; and Polybutadiene Rican 156 has a number average molecular weightof 1400; or Polybutadiene LBR307, LBR305 commercially available fromKURARAY CO., LTD; the number average molecular weight thereof are about8000 and 26000, respectively.

Most preferably, the liquid polybutadiene is selected from the groupconsisting of: PB-3600 from Daicel Chemical co., and Ricon130polybutadiene from Sartomer Company, Inc.

In the adhesive composition of the present invention, based on the totalweight of the adhesive composition, the amount of liquid polybutadieneused may be 0-50 wt %, preferably 10-40 wt %, more preferably 20-35 wt%.

“Other Components”: In addition to above components, the adhesivecomposition according to the present invention may optionally containother additives well known to those skilled in the art, for example, nonlimiting to: light stabilizer, thermal stabilizer, promoter to photoinitiation, promoter to thermal initiation, level agent, tougheningagent, thickening agent, and etc.

Based on the total weight of said adhesive composition, said additivesmay account for 0.01-1 wt %, or 1%-2 wt %, or 0-2 wt %.

“Substrate to be bonded”: The present inventive adhesive composition isparticularly suitable for bonding touch screen and substrate ofelectronic devices. Non-limited examples of the electronic devicesinclude mobile phone, television, palm PDA, notebook, table PC, andother devices having a touch screen. The touch screen may be any type ofpanel in the art, for example, liquid crystal display panel, plasmadisplay panel, and organic electroluminescent panel, and the like.

The substrate may be any type in the art as well, generally it includesglass or polymeric material. Useful glass comprises, but not limitingto, borosilicate glass, soda-lime glass, and any other glasses suitablefor display screen. Useful polymeric material includes polyester film,for example polyethylene terephthalate PET, polycarbonate film orpolyacrylate film, for example, polymethyl methacrylate film, andcycloolefin polymeric film, for example, ZEONOX and ZEONOR from ZeonChemicals L. P. Said substrate preferably has a reflective indexcomparable with those of display screen, for example, from about 1.4 toabout 1.7. Typical thickness of substrate may be about 0.5 to about 5mm.

“Production of Adhesive”: The adhesive composition in accordance withthe present invention may be prepared as follows: into a mixingcontainer with conventional stirring means, under the condition ofsubstantially complete darkness, in a predetermined ratio, eachcomponents of the adhesive composition are fed into and mixed. Mixing isusually conducted at ambient temperature, or a temperature slightlyhigher or lower than ambient temperature. Mixing should last for asufficient time to ensure a uniformly dispersed components, thusobtaining the adhesive composition. Store the thus obtained adhesivecomposition in dark environment, for subsequent bonding between touchscreen and substrate.

The volume of the mixing container is not specifically defined, perspecific requirements, it could be, for example, about 1-100 L, or 5-50L, or 10-30 L, and etc. The mixing container could be such as thosecommercially available; with a conventional stirring means, such as,paddle stirrer, anchor stirrer, propeller stirrer and the like, thespeed of rotation generally depends from the type of the stirrer and theviscosity of adhesive components, and etc. For example. It could be 10rpm-500 rpm, or 50 rpm-300 rpm, or rotor-stator stirrer may also beadopted, with a speed of rotation of, for example, 300-4000 rpm,preferably 1500-3000 rpm. For example, the mixing time could be about1-10 minutes, or 2 to 8 minutes, or 4-6 minutes and etc; thus obtainingthe adhesive composition.

“UV Cure”: After the touch screen and substrate is bonded with theadhesive composition in accordance with the present invention, thebonded assembly should be cured. As to the UV cure of the bondedassembly, UV source covering the range of 200 nm-400 nm wavelength couldbe adopted, for example, with an irradiation power of 100 mW/cm². Perspecific requirements, irradiation could be conducted for seconds totens of seconds, for example 5-30 seconds, or even longer. Theirradiation power and time could be easily determined by those skilledin the art per the requirements of products.

The present invention may take use of commercially available lampassembly, including an arc lamp, for example, please refer to thosedisclosed in U.S. Pat. No. 6,520,663 and 6881964, the contents thereofare incorporated here by reference. UV cure oven may also be adopted,for example, Loctite UVALOC 1000 from Henkel AG.

“Thermal Cure”: After UV cure, the bonded sample will be further thermalcured. Thermal cure may be conducted by any conventional means in theart without any limitation. For example, it may be performed by using anoven with a hot air circulating oven with adjustable temperaturecontroller. The specific thermal cure temperature may be, for example50-150° C., or 60-140° C., 70-120° C., most preferably 80-90° C. Thetime of thermal cure depends on the specific adhesive composition, forexample, in case of high content of thermal initiator, cure time couldbe relatively short, such as 30 minutes to 1.5 hours, and in case of lowcontent of thermal initiator, cure time could be relatively long, suchas 1-3 hours.

“Testing Methods involved in the present invention”: In accordance withthe present invention, specifically, testing methods involved aredescribed as follows:

1. Viscosity: Viscosity is used to describe the flowing resistance of aliquid, and in principle, it reflects the inner molecular friction. Inthe present invention, the testing instrument used to measure theviscosity of uncured adhesive composition may be commercially availableBrookfield rotating viscosity meters, and testing temperature is ambienttemperature (about 25° C.), or room temperature, or 60° C. and etc., andthe testing may preferably be performed per the specification in ASTMD1086-1997. The unit of viscosity is poise or centipoise. Preferably,viscosity is measured at 25° C. at a shear rate of 2.55 s⁻¹ by HAAKERotational Rheometer with a cone plate (35 mm diameter).

2. Light Transmittance: Light transmittance is an index to describe thetransmission of light through a material, typically, it is expressed asa ratio of intensity of transmissive light I_(t) to intensity ofincident light I₀. After complete cure, the testing of lighttransmittance of the adhesive composition may typically measured byconventional commercially available UV light spectrophotometer. Thethickness of the two pieces of testing samples adopted in the adhesivecomposition may be controlled in a certain range, for example, about 100μm.

Testing of light transmittance may preferably be conducted according tothe specification in ASTM D1005-2007.

Preferably an adhesive is regarded as optically transparent, if itexhibits an optical transmission of at least 85%.

3. Bonding Strength: Bonding strength is used to characterize thejoining strength between two pieces of bonded materials, after thebonding between the samples are sufficiently cured.

The thickness of the adhesive coating generally is controlled perspecific requirements, such as at about 100 μm. Substrate may beselected, per requirements, as glass sheet, acrylate resin sheet, orpolyester sheet. In the present testing, the size of glass substratesample is typically of 100 mm long, 10 mm wide and 2 mm thick.

Testing equipment for bonding strength may preferably be an universaltensile machine, the mode thereof may be, for example, Instron 5569 fromInstron Inc.

For example, the procedure for measuring the bonding strength is, forexample, as follows: dropping the adhesive to be tested in one of thecenter of a piece of glass sheet, copper wire having 100 um in diameteris disposed at two sides of the adhesive for the purpose of controllingthe thickness thereof. Then another piece of glass is lapped verticallyabove the adhesive, forming a lapping sample in cross form. The lappedsample is further put into a UV cure oven (for example, Loctite UVALOC1000, Henkel AG) to carry out UV cure. Predetermined condition is:irradiation for 30 seconds, the power thereof is 100 mW/cm².

The cured sample is further placed at room temperature for 24 hours,then universal tensile machine is used to tensile the bonded samplevertically in opposed direction. The tensile speed may be set as 2inches/min. The bonding strength (unit: MPa) could be obtainable viadividing the value of force recorded in the machine by the lapping area.

4. Molecular Weight: Molecular weight of the starting materials of theadhesive composition includes number average molecular weight, weightaverage molecular weight, and the like. Unless indicated otherwise,measurement of said molecular weight is conducted by using gelpermeation chromatography (GPC) well known and widely adopted in therelevant art. In the measurement, polystyrene having a narrow molecularweight distribution may be used as standard, for example, andtetrahydrofuran may be used as the mobile phase, and the flowing speed,for example, may be 0.8 mL/min, and the column temperature for example,may be 35° C.

EXAMPLES

Hereafter examples are provided to further describe the presentinvention, said examples are only for illustration to the presentinvention; rather, it should not be construed as a limitation to thepresent invention.

Specific Testing Conducted in Examples Test 1: UV Cure Experiment

At room temperature, a UV light source covering the emitting wavelengthof 200 nm-400 nm, having an irradiation power of 100 mW/cm² was used toirradiate the boding of adhesive composition between glass andpolycarbonate (PC) sheets for 30 seconds.

Test 2: Thermal Cure Experiment

Under the condition of darkness, in an oven with an adjustabletemperature controller, the highest temperature thereof was no less than200° C., the adhesive composition between glass and PC sheets wasthermal cured. The cure time depended on specific components of theadhesive composition.

Test 3: Bonding Strength Experiment

In the present invention, under the condition of 100 mW/cm² UVAirradiation, the adhesive composition between glass sheet and glasssheet was cured for 30 seconds, and according to the above mentionedtesting method, the bonding strength of the adhesive composition wasmeasured.

Test 4: Light Transmittance Experiment

An UV light-visible light spectrophotometer was adopted to measure thelight transmittance of the adhesive material after curing. The thicknessof the cured adhesive material was controlled at about 100 μm. Testingmethod was per the specification of ASTM D1005-2007. After theirradiation of 100 mW/cm² UVA for the adhesive composition between glassand glass sheets for 30 seconds, the light transmittance of the adhesivecomposition was measured accordingly.

Test 5: Shadow Area Checking

Kept the area applied by adhesive composition or the lapped area betweenthe testing sheets in complete darkness. After such an arrangement,thermal cure of the adhesive composition was conducted. After thethermal cure testing condition was met, checked the results of the bodyto be bonded.

Raw materials used Components Products urethane oligomer having Genomer4188/EHA (Rahn AG): mixture consisting of 80 (meth)acryloxy group 1-1wt. % of a monoacrylate-functional polyesterbased oligomer comprising atleast one urethane bond, and 20% 2-ethylhexyl acrylate monomers; theoligomer comprised by GENOMER 4188 has a weight average molecular weightMw of about 8,000, average degree of functionality about 1, viscosity at25° C.: about 70000 cps, Tg: about −3° C. urethane oligomer having CN9021 (Sartomer Company, Inc.), average degree of (meth)acryloxy group1-2 functionality: 2, viscosity at 25° C.: about 32000 cps, Tg: −54° C.urethane oligomer having CN 8004 (Sartomer Company, Inc.); averagedegree of (meth)acryloxy group 1-3 functionality: less than 2, viscosityat 60° C.: about 9000 cps, Tg: about −3° C. polyisoprene having UC-102(Kuraray Company), average degree of methacryloxy group 2-1functionality: 2, number average molecular weight: about 17,000, Tg:−60° C. polyisoprene having UC-203 (Kuraray Company), average degree ofmethacryloxy group 2-2 functionality: 3, number average molecularweight: about 35,000, Tg: −60° C. liquid polybutadiene 3-1 Ricon130(Sartomer Company, Inc.), number average molecular weight: about 2500(meth)acrylate monomer 4-1 commercially available isobornyl acrylate(meth)acrylate monomer 4-2 commercially available hydroxypropylmethacrylate (meth)acrylate monomer 4-3 commercially available2-(2-ethoxyethoxy)ethyl acrylate (meth)acrylate monomer 4-4 commerciallyavailable ethylene glycol dicyclopentenyl ether methacrylateUV-photoinitiator 5-1 2-hydroxy-2-methyl-1-phenyl-1-propanone (BASFcompany, Inc.) UV-photoinitiator 5-2diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide (BASF company, Inc.)thermal initiator 6-1 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane (J&K Scientific Ltd.) thermal initiator 6-2 tert-butylperoxybenzoate

Other compounds used in the examples are all chemical pure reagents, andare all commercially available.

Example 1 Inventive

Adhesive composition 1 was formulated according to the composition inTable 1 and formulating method as stated below:

TABLE 1 Components Contents urethane oligomer having (meth) 70 parts byweight acryloxy group 1-1 (meth)acrylate 4-1 10 parts by weight(meth)acrylate 4-2  7 parts by weight (meth)acrylate 4-3  7 parts byweight UV-photoinitiator 5-1  2 parts by weight UV-photoinitiator 5-2  1parts by weight thermal initiator 6-1  2 parts by weight thermalinitiator 6-2  1 parts by weight

The formulating procedure of the adhesive composition was as follows:Under a condition of darkness, feeding all above components (total: 100g) into a plastic barrel having a volume of 150 g in the order listedabove, mounting a SpeedMixer™ mixer produced by FlackTech Inc. in thebarrel, and all the components were mixed and dispersed at a rotation of2000-2400 rpm for 10 minutes, thus obtaining a transparent adhesivecomposition 1.

Example 2 Inventive

Adhesive composition 2 was formulated according to the composition inTable 2 and method as stated in example 1.

TABLE 2 Components Contents urethane oligomer having (meth) 70 parts byweight acryloxy group 1-1 (meth)acrylate 4-1 11 parts by weight(meth)acrylate 4-2  7 parts by weight (meth)acrylate 4-3  7 parts byweight UV-photoinitiator 5-1  2 parts by weight UV-photoinitiator 5-2  1parts by weight thermal initiator 6-1  2 parts by weight

Example 3 Not Inventive

Adhesive composition 3 was formulated according to the composition inTable 3 and method as stated in example 1.

TABLE 3 Components Contents urethane oligomer having (meth) 70 parts byweight acryloxy group 1-1 (meth)acrylate 4-1 11 parts by weight(meth)acrylate 4-2  8 parts by weight (meth)acrylate 4-3  8 parts byweight UV-photoinitiator 5-1  1 parts by weight

Example 4 Inventive

Adhesive composition 4 was formulated according to the composition inTable 4 and method as stated in example 1.

TABLE 4 Components Contents urethane oligomer having (meth) 65 parts byweight acryloxy group 1-2 urethane oligomer having (meth) 20 parts byweight acryloxy group 1-3 (meth)acrylate 4-1 10 parts by weight(meth)acrylate 4-2  7 parts by weight (meth)acrylate 4-3  7 parts byweight UV-photoinitiator 5-1  2 parts by weight thermal initiator 6-1  2parts by weight thermal initiator 6-2  1 parts by weight

Example 5 Inventive

Adhesive composition 5 was formulated according to the composition inTable 5 and method as stated in example 1.

TABLE 5 Components Contents urethane oligomer having (meth) 65 parts byweight acryloxy group 1-2 urethane oligomer having (meth) 20 parts byweight acryloxy group 1-3 (meth)acrylate 4-1 10 parts by weight(meth)acrylate 4-2  7 parts by weight (meth)acrylate 4-3  7 parts byweight UV-photoinitiator 5-1  2 parts by weight UV-photoinitiator 5-2  1parts by weight thermal initiator 6-1  2 parts by weight

Example 6 Inventive

Adhesive composition 6 was formulated according to the composition inTable 6 and method as stated in example 1.

TABLE 6 Components Contents polyisoprene having 30 parts by weightmethacryloxy group 2-1 liquid polybutadiene 3-1 40 parts by weight(meth)acrylate 4-1 12 parts by weight (meth)acrylate 4-2 12 parts byweight UV-photoinitiator 5-1  2 parts by weight UV-photoinitiator 5-2  1parts by weight thermal initiator 6-1  2 parts by weight thermalinitiator 6-2  1 parts by weight

Example 7 Inventive

Adhesive composition 7 was formulated according to the composition inTable 7 and method as stated in example 1.

TABLE 7 Components Contents Polyisoprene having 30 parts by weightmethacryloxy group 2-1 liquid polybutadiene 3-1 40 parts by weight(meth)acrylate 4-2 12 parts by weight (meth)acrylate 4-4 12 parts byweight UV-photoinitiator 5-1  2 parts by weight UV-photoinitiator 5-2  1parts by weight thermal initiator 6-1  2 parts by weight thermalinitiator 6-2  1 parts by weight

Example 8 Not Inventive

Adhesive composition 8 was formulated according to the composition inTable 8 and method as stated in example 1

TABLE 8 Components Contents Polyisoprene having methacryloxy 30 parts byweight group 2-1 polyisoprene having methacryloxy 10 parts by weightgroup 2-2 liquid polybutadiene 3-1 33 parts by weight (meth)acrylate 4-112 parts by weight (meth)acrylate 4-2 12 parts by weightUV-photoinitiator 5-1  2 parts by weight UV-photoinitiator 5-2  1 partsby weight

Example 9 Inventive

Adhesive composition 9 was formulated according to the composition inTable 9 and method as stated in example 1.

TABLE 9 Components Contents polyisoprene having 50 parts by weightmethacryloxy group 2-1 (meth)acrylate 4-1 12 parts by weight(meth)acrylate 4-2 12 parts by weight (meth)acrylate 4-4 20 parts byweight UV-photoinitiator 5-1  2 parts by weight UV-photoinitiator 5-2  1parts by weight thermal initiator 6-1  2 parts by weight thermalinitiator 6-2  1 parts by weight

Example 10 Inventive

Adhesive composition 10 was formulated according to the composition inTable 10 and method as stated in example 1.

TABLE 10 Components Contents polyisoprene having 45 parts by weightmethacryloxy group 2-1 polyisoprene having 15 parts by weightmethacryloxy group 2-2 (meth)acrylate 4-1 17 parts by weight(meth)acrylate 4-4 17 parts by weight UV-photoinitiator 5-1  2 parts byweight UV-photoinitiator 5-2  1 parts by weight Thermal initiator 6-1  2parts by weight Thermal initiator 6-2  1 parts by weight

The adhesive compositions 1-10 of Examples 1-10 were tested as mentionedin test 1 to test 5, and the results were showed in Table 11 below:

TABLE 11 Example 1 Example 2 Example 3 Example 4 Example 5 test 1 curedwithin cured within cured within cured within cured within 30 seconds 30seconds 30 seconds 30 seconds 30 seconds test 2 cured within 1 curedwithin 2 Could not cured within 1 cured within 2 hour at 80° C. hours at90° C. cured hour at 80° C. hours at 90° C. test 3 >0.6 MPa >0.6MPa >0.6. MPa >0.4 MPa >0.4 MPa test 4 >92% >92% >92% 92% 92% test 5composition composition composition composition composition cured curedin liquid cured cured Example 6 Example 7 Example 8 Example 9 Example 10test 1 cured within cured within cured within cured within cured within30 seconds 30 seconds 30 seconds 30 seconds 30 seconds test 2 curedwithin 1 cured within 2 Could not cured within 1 cured within 2 hour at80° C. hours at 90° C. cured hour at 80° C. hours at 90° C. test 3 >0.6MPa >0.6 MPa >0.6.MPa >0.4 MPa >0.4 MPa test 4 >92% >92% >92% 92% 92%test 5 composition composition composition composition composition curedcured in liquid cured cured

1-2. (canceled)
 3. An optical transparent dual cure adhesivecomposition, based on the total weight of the adhesive composition, thecomposition comprises: 40-90 wt % of urethane oligomer having(meth)acryloxy group; 5-55 wt % of (meth)acrylate; 0.5-5 wt % ofUV-photoinitiator; and 0.5-5 wt % of thermal initiator.
 4. Thecomposition according to claim 3, characterized in that, said urethaneoligomer having (meth)acryloxy group has an average degree offunctionality of more than 0 and equal to or less than 3, preferablyfrom 0.5 to 2.5; and the glass transition temperature T_(g) thereof isfrom −80 to 0° C., preferably from −60 to 0° C., and the Brookfieldviscosity thereof at the temperature of 25° C. preferably is from 1000cps to 190000 cps, more preferably from 2000 cps to 150000 cps.
 5. Thecomposition according to claim 3, characterized in that, based on thetotal weight of the adhesive composition, the composition comprises50-80 wt % of urethane oligomer having (meth)acryloxy group, preferably60-70 wt %; 10-50 wt % of (meth)acrylate, preferably 20-40 wt %; 1-4 wt% of UV-photoinitiator, preferably 2-3 wt %; 1-4 wt % of thermalinitiator, preferably 2-3 wt %.
 6. The composition according to claim 3,characterized in that, said urethane oligomer having (meth)acryloxygroup has number average molecular weight of 1000-25000 Daltons,preferably 1500-10000 Daltons.
 7. An optical transparent dual cureadhesive composition, based on the total weight of the adhesivecomposition, the composition comprises: 10-80 wt % of polyisoprenehaving (meth)acryloxy group or vinyl group; 10-55 wt % of(meth)acrylate; 0-50 wt % of liquid polybutadiene, 0.5-5 wt % ofUV-photoinitiator, and 0.5-5 wt % of thermal initiator.
 8. Thecomposition according to claim characterized in that, said polyisoprenehaving (meth)acryloxy group or vinyl group has an average degree offunctionality of 0.5-3, a number average molecular weight of 10000-50000Daltons, preferably 12000-40000 Daltons, more preferably 15000-35000Daltons; and said liquid polybutadiene preferably has a number averagemolecular weight of 1000-30000 Daltons; more preferably 1500-25000Daltons, even more preferably 2000-20000 Daltons, particularlypreferably 3000-10000 Daltons.
 9. The composition according to claim 7,characterized in that, based on the total weight of the adhesivecomposition, the adhesive composition comprises 20-70 wt % ofpolyisoprene having (meth)acryloxy group or vinyl group, preferably30-60 wt %; 10-40 wt % of liquid polybutadiene, preferably 20-35 wt %;20-45 wt % of (meth)acrylate, preferably 25-40 wt %; 1-4 wt % ofUV-photoinitiator, preferably 2-3 wt %; and 1-4 wt % of thermalinitiator; preferably 2-3 wt %. 10-15. (canceled)